Different SW versions lead to very inconsistent results

[Shuo]

Hi,

I have built a RFQ electrode model and got the 3D ES field by CST EM Studio.
But I have encourtered a problem when i run the same one input(same .ini, .dat, .edx, edy, edz...) on different sw versions(2.18.02 and 2.24.04).

Below is from sw version 2.18.02 :

1.PNG (523.63 KiB) Viewed 1014 times

And if merge the two longitudinal phase space ellispe into one, it will become:

2.png (650.92 KiB) Viewed 1014 times

But when i perform the same action on sw version 2.24.04, the transverse phase space will be much different:

3.PNG (496.37 KiB) Viewed 1014 times

The merged longitudinal phase space is as below:

4.PNG (735.76 KiB) Viewed 1014 times

And for longitudinal phase space, the alpha is also much different:

5.PNG (430.43 KiB) Viewed 1014 times

alpha is -0.2775 in sw version 2.18.02; alpha is -0.4511 in sw version 2.24.04.


Is there any setting that i missed in new sw version?

Than you for any help.

Shuo

[Didier]

Dear Shuo,

I can't explain the difference you're seeing and none of my own simulations show such differences. You'll have to send me your files so that I can understand what the problem is.

Regards,

Didier

[Shuo]

Dear Didier,

Thank you for your response. I appreciate your willingness to look into the issue. I will send you the files as attachments. Please let me know if you need any additional information or have further questions.

Thank you again for your assistance.

Best regards,

Shuo

[Didier]

Hi,

OK, I think the problem is that the input distributions are not the same.
It's too complicated at the moment, away from my desk, to understand why. I'll check it out when I get back, in the last week of August.

Regards,

Didier

[Shuo]

Hi Didier,

Thank you for your response. Please let me know if there is any additional data I can provide to assist you with your investigation. I look forward to hearing from you once you have had the opportunity to review the situation further.

Thank you again for your support.

Best regards,

Shuo

[Didier]

Dear Shuo,

OK, I've found the reason for the observed difference and it has nothing to do with my first explanation about the input distribution. It comes from an improvement made to the space-charge calculation, carried out by a colleague.
However, in your case, is the difference significant and I'm still wondering about this modification and my colleague hasn't returned from leave yet, so as soon as he comes back I'll discuss it with him and see whether or not it actually leads to a significant difference and is justified.
I'll keep you informed asp via this discussion.

Regards,

Didier

[Didier]

Dear Shuo,

Ok, without waiting for my colleague to get back to me, I've made a few corrections in TraceWin to improve the situation considerably, but there are probably a few points that will need to be checked later here between space-charge experts. These changes have been incorporated into the latest update of TraceWin.
Another important point is that you need to adjust the RF phase of the field card to avoid the multi-bunch effect at the RFQ output that you have with the latest version of TraceWin. I suggest that you set the field map RF phase to -50° instead of 180°.

Regards,

Didier

[Shuo]

Dear Didier,

Thank you for the update and the corrections you’ve made in TraceWin. I’ll proceed with some tests using the new settings, adjusting the RF phase of the field card to -50° as you suggested. I’ll analyze the results to see if it works out.

Once I have more data, I’ll get back to you.

Best regards,

Shuo

[Shuo]

Dear Didier,

Great! The difference of the transverse phase space is solved in the latest updated TraceWin.
For the multi-bunch effect at the RFQ output, there still seems to be multiple bunches at the RFQ output when i adjusted the RF phase of the field card to -50° as you suggested.
The original phase space at RFQ output is as below:

org_output.png (526.87 KiB) Viewed 410 times

The merged phase space at RFQ output is as below:

merged_output.png (737.99 KiB) Viewed 410 times

Thank you very much for your assistance in resolving this issue.

Best regards,

Shuo

[Didier]

Dear Shuo,

I wanted to inform you that in the latest version of TraceWin, after discussions with experts, I went back on the changes to the space-charge calculation that I had made following our exchange. In the end, these changes were not appropriate and it was the RF phase change that was the cause of the main differences observed with an older version.
So this step backwards will slightly change your simulation results, but from my point of view they will be more accurate.

Regards,

Didier